An Investigation into the Physiological Role of Annexin A11

Annexin A11 is a ubiquitously expressed member of the annexin family of Ca2+-dependent phospholipid binding proteins, which lies at the root of the vertebrate annexin evolutionary tree. Annexin A11 is known to be localised to the nuclei of cells in culture, and to interact Ca2+-dependently in vitro with the S100 protein S100A6 and the penta EF-hand protein ALG-2 through its long glycine, proline and tyrosine-rich N-terminal domain, but very little is known about the physiological functions performed by this annexin in vivo. An investigation into the cellular roles of annexin A11 both in interphase and during cell division is presented in this thesis. Using various molecular and cell biology approaches, annexin A11 was identified in the nucleus and in cytoplasmic vesicles that appear to be transported along the microtubular network, linking annexin A11 function with intracellular membrane trafficking processes. Annexin A11 has also been identified in membrane domains involved in signal transduction at the basolateral membrane of A431 cells. A role for this annexin in membrane remodelling steps during cell growth is proposed in view of the accumulation of annexin A11-containing vesicles in the cytoplasm of non-contact inhibited cells and at the leading edge of monolayer outgrowths, together with the concentration of annexin A11 at the cell-cell contact sites in the plasma membrane of confluent monolayers. Annexin A11 relocates to the nuclear envelope and is tyrosine-phosphorylated in the presence of calcium in interphase cells, and invades the nuclear envelope at the invaginations created during nuclear envelope breakdown at the onset of mitosis, and is also detected at the nuclear envelope during nuclear envelope reassembly after cell division, making the nuclear envelope a specific target for annexin A11. The study of the function of annexin A11 during cell division led to the identification of an essential role for annexin A11 in the terminal phase of cytokinesis. Annexin 11 was observed to translocate from the nucleus to the spindle poles in metaphase, and then to the spindle midzone in anaphase, and to be recruited to the midbody in late telophase where it co-localises and associates with the mitotic kinesin- like protein CHO1. Depletion of annexin A11 by RNA interference has shown that the absence of this annexin leads to failure to establish a functional midbody, incomplete daughter cell separation, and ultimately cell death by apoptosis